In general, a light-colored soy sauce, a so-called usukuchi shoyu was prepared using wheat as a starchy raw material and soybeans as a protein raw material. In the process, the starchy raw material was charged in somewhat larger amount or a common salt was charged with higher salt concentration to inhibit coloration. As a result, the prior usukuchi shoyu felt rather salty than tasty.
Further, the prior usukuchi shoyu has a very rapid browning rate, is unstable and also has an unsatisfactory flavor due to the processes employing a shortened fermenting and decoloration of the resultant soy sauce to obtain a light color.
For manufacture of a light-colored soy sauce having a slow browning rate, it is suggested in Japanese Patent Publication No. Sho 57-48188 that at least one of starchy materials from corn, sorghum and millet is used in combination with 10-30% by weight of gluten.
However, this process has the problems that (i) a peculiar flavor derived from wheat cannot be felt, since other starchy materials than wheat are used, (ii) corn, sorghum or millet has a less glutamic acid content, then a glutamic acid content in soy sauce becomes less and as a result, a poor taste is given, and (iii) soy sauce is not so much light-colored.